The invention is directed to a method for controlling the transmission power of a mobile station in a mobile cellular radio network having base stations in a mutual spatial arrangement.
Co-channel interference and adjacent channel interference have a primary influence on the reception quality of the useful signal in cellular mobile radio networks. In order to keep these co-channel and adjacent channel disturbances to an optimally low level, the transmission power of the mobile station and/or of the base station can be controlled, taking the channel quality into consideration. A reduction of the transmission power of radio links with high channel quality to a level at which an adequate reception quality is still assured leads to a reduction of the co-channel and adjacent channel interference on other radio links, and thus leads to an improvement of the reception quality of these radio links. By improving the interference situation in cellular mobile radio networks, the frequency reuse distance can be reduced, and thus the capacity of the network can be enhanced.
It is also important for the mobile station to reduce the transmission power to a minimally required level in order to efficiently manage the existing energy. This enables a longer operating duration or smaller, lighter mobile device as well.
The control of the transmission power of the mobile station should occur as currently and as exactly as possible in order to keep the reception quality of the data at a defined level. The co-channel and adjacent channel interference can thereby be efficiently reduced and the energy of the mobile station can be economically utilized.
The considerable time-lag between measurement acquisition and adaptation of the transmission power has proven problematical in previous methods. In, for example, GSM, approximately two seconds elapse from the acquisition of the first measured value in the base station up to the adaptation of the transmission power of the mobile station, and even up to three seconds under certain circumstances. When, for example, the mobile station is moving at a speed of 30 km/h, then it covers 8.4 m in one second; i.e., given wavelengths of a few centimeters (GSM:f=900 MHz.rarw..fwdarw..lambda.=33 cm, UMTS:f=2000 MHz.rarw..fwdarw..lambda.=15 cm), the propagation conditions, and thus the channel quality, have meanwhile changed significantly. Consequently, an adaptation of the transmission power occurs to propagation conditions that are not any longer relevant. An almost delay-free control of the transmission power of the mobile station is therefore desirable.
On the other hand, the repetition period of the adaptation may not be reduced arbitrarily because of a necessary minimum measuring period in order to not destabilize the system due to fast and local variations of the propagation conditions. A tracking of the fast fading (Rayleigh, Rice) would lead to instability of the system. The effects of the fast fading are therefore to be filtered out (for example, on the basis of a suitable averaging) so that the control algorithm is effective for path loss and slow fading that mainly arises due to shadowing and reflections.